Roller reducers are a subset of planetary reducers and can be used for adjusting torque and as a rotation/linear motion converters. In particular, roller reducers can be used in robots, manipulators and power drives requiring transmission of large amounts of torque under size restrictions. Such reducers have the following advantages: simple design and few components; high kinematic accuracy provided by a short kinematic chain and many contact points; smooth and low-noise operation; small dimensions while providing high transmitted torque; and operation at high input shaft rotation velocities.
Inventor's Certificate SU 1294606 discloses a manipulator joint formed by a roller reducer; the joint comprises a threaded shaft and threaded rollers forming a planetary gear, and first and second members comprising nuts, wherein the first member is formed by a fork embracing the second member. First member nuts are engaged with the roller threads, which in turn are engaged with the shaft threads, and second member nuts are engaged with the output roller threads. According to SU 1294606, play is eliminated in all thread engagements in said manipulator joint by pressing the reducer members together.
A disadvantage of SU 1294606 is that the rollers tend to bend in the central or proximal part thereof along the shaft upon transmitting high torque, which leads to a shift of contact points towards thread edge and to edge contact, leading to a decreased load-bearing capacity of the reducer, greater slip and worse efficiency.
Further, SU 1294606 disadvantageously prevents from providing a play-free transmission because pressing together nuts of each of the members, to allegedly eliminate play in thread interfaces, can cause slip of the rollers, and the play will persist.
Thus, it is an object of the present invention to provide a transmission gear and a roller reducer comprising fewer components, but presenting stable characteristics across the whole load range, and a wide range of gear ratios obtained by adjusting parameters of reducer elements without adding and removing extra elements.
Furthermore, it is an object of the present invention to increase load-bearing capabilities and efficiency of the reducer, and to provide play-free transmission.
A further object of the present invention is to provide a method for faultless assembly of the reducer at minimum labor cost.